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Abstract:

A screen including a first liquid crystal layer area including a polymer
dispersion liquid crystal material and capable of switching a state of
the first liquid crystal layer area between a transmission state and a
scatter state based on voltage application and a second liquid crystal
layer area provided outside the first liquid crystal layer area,
including a liquid crystal material and a dichromatic dye, and capable of
switching a state of the second liquid crystal layer area between a
transmission state and a colored state based on voltage application.

Claims:

1. A screen comprising: a first liquid crystal layer area including a
polymer dispersion liquid crystal material and capable of switching a
state of the first liquid crystal layer area between a transmission state
and a scatter state based on voltage application; and a second liquid
crystal layer area provided outside the first liquid crystal layer area,
including a liquid crystal material and a dichromatic dye, and capable of
switching a state of the second liquid crystal layer area between a
transmission state and a colored state based on voltage application.

2. The screen according to claim 1, wherein the screen is capable of
operating in a first state in which the first liquid crystal layer area
operates in the scatter state and the second liquid crystal layer area
operates in the colored state, and a second state in which the first and
second liquid crystal layer areas both operate in the transmission state,
and an image is displayed in the first liquid crystal layer area that
operates in the first state.

3. The screen according to claim 1, wherein the voltages are applied by
common electrodes to the first and second liquid crystal layer areas.

4. The screen according to claim 2, wherein the first state is produced
when the voltages are applied, and the second state is produced when no
voltage is applied.

5. The screen according to claim 2, wherein the second state is produced
when the voltages are applied, and the first state is produced when no
voltage is applied.

6. The screen according to claim 1, wherein the voltages are applied by
different electrodes independently of each other to the first and second
liquid crystal layer areas.

7. The screen according to claim 1, wherein a color displayed in the
colored state is black.

8. An image display system comprising: the screen according to claim 1; a
projector that displays an image on the screen; and a controller that
controls operation of driving the screen and the projector.

9. The image display system according to claim 8, wherein the controller
instructs the screen to operate in the first state, in which the first
liquid crystal layer area operates in the scatter state and the second
liquid crystal layer area operates in the colored state, in response to
outputting an image signal to the projector.

10. An image display system comprising: the screen according to claim 2;
a projector that displays an image on the screen; and a controller that
controls operation of driving the screen and the projector.

11. The image display system according to claim 10, wherein the
controller instructs the screen to operate in the first state in response
to outputting an image signal to the projector.

12. An image display system comprising: the screen according to claim 3;
a projector that displays an image on the screen; and a controller that
controls operation of driving the screen and the projector.

13. The image display system according to claim 12, wherein the
controller instructs the screen to operate in the first state, in which
the first liquid crystal layer area operates in the scatter state and the
second liquid crystal layer area operates in the colored state, in
response to outputting an image signal to the projector.

14. An image display system comprising: the screen according to claim 4;
a projector that displays an image on the screen; and a controller that
controls operation of driving the screen and the projector.

15. The image display system according to claim 14, wherein the
controller instructs the screen to operate in the first state in response
to outputting an image signal to the projector.

16. An image display system comprising: the screen according to claim 6;
a projector that displays an image on the screen; and a controller that
controls operation of driving the screen and the projector.

17. The image display system according to claim 16, wherein the
controller instructs the screen to operate in the first state, in which
the first liquid crystal layer area operates in the scatter state and the
second liquid crystal layer area operates in the colored state, in
response to outputting an image signal to the projector.

18. An image display system comprising: the screen according to claim 7;
a projector that displays an image on the screen; and a controller that
controls operation of driving the screen and the projector.

19. The image display system according to claim 18, wherein the
controller instructs the screen to operate in the first state, in which
the first liquid crystal layer area operates in the scatter state and the
second liquid crystal layer area operates in the colored state, in
response to outputting an image signal to the projector.

Description:

BACKGROUND

[0001] 1. Technical Field

[0002] The present invention relates to a screen and an image display
system.

[0003] 2. Related Art

[0004] There have been known technologies for displaying video images from
a projector or any other apparatus on a screen. In recent years, there
has been a proposed technology for displaying video images by using a
screen capable of switching its state between a transmission
(transparent) state and a scatter state and projecting video image light
on the screen that operates in the scatter state. Using the technology to
set the screen to be transparent when no video image is projected reduces
a feeling of spatial oppression produced by the screen not in use. A
screen capable of switching its state between the transmission
(transparent) state and the scatter state by using a liquid crystal layer
has been proposed (JP-A-6-82748, for example) as an example of the screen
described above.

[0005] As the technology for switching the state of a screen between the
transmission (transparent) state and the scatter state by using a liquid
crystal layer, there is a known polymer dispersion liquid crystal display
apparatus in which a liquid crystal material is dispersed in a polymer
(JP-A-10-36317, for example). The principle according to which a polymer
dispersion liquid crystal display apparatus of this type operates uses
the difference in refractive index between the liquid crystal material
and the polymer. In a normal mode, the transmission (transparent) state
is created by applying an electric field, and the scatter state is
created by removing the electric field. In a reverse mode, the
transmission (transparent) state is created by applying no electric
field, and the scatter state is created by applying an electric field.
When the polymer dispersion liquid crystal display device is used as a
screen, and video image light is projected on the screen that operates in
the scatter state, a desired image is displayed on the screen. In the
scatter state, however, surrounding external light is also scattered and
disadvantageously decreases the contrast of the displayed image.

[0006] To suppress the decrease in contrast described above, there is a
known method for introducing a black dichromatic dye into a polymer
dispersion liquid crystal material. The method prevents surrounding
external light from being scattered and the contrast of an image from
being degraded. In a screen (polymer dispersion liquid crystal display
device) into which a dichromatic dye is introduced, however, the
dichromatic dye does not respond sufficiently fast because the motion of
the dichromatic dye is restricted in the polymer. The reason for this is
that a dichromatic dye is driven based on a guest-host effect, but the
motion of the dichromatic dye is restricted when a polymer is present.

[0007] When the problem described above occurs, the transmittance of the
screen (polymer dispersion liquid crystal display device) in the
transmissive (transparent) state decreases, resulting in a difficulty in
achieving a sufficiently transparent state.

SUMMARY

[0008] An advantage of some aspects of the invention is to provide a
screen and an image display system capable of enhancing a contrast
sensation based on a visual effect of human eyes and providing excellent
transparency in a transmission state. A screen according to an aspect of
the invention includes a first liquid crystal layer area including a
polymer dispersion liquid crystal material and capable of switching a
state of the first liquid crystal layer area between a transmission state
and a scatter state based on voltage application and a second liquid
crystal layer area provided outside the first liquid crystal layer area,
including a liquid crystal material and a dichromatic dye, and capable of
switching a state of the second liquid crystal layer area between a
transmission state and a colored state based on voltage application.

[0009] In the screen described above, an image is displayed in the first
liquid crystal layer area that operates in the scatter state, and the
image is surrounded by the second liquid crystal layer area that operates
in the colored state. The second liquid crystal layer area that operates
in the colored state and surrounds the image gives an increased contrast
sensation based on a visual effect of human eyes. Further, since the
second liquid crystal layer area contains no polymer, the dichromatic dye
can be appropriately moved based on a guest-host effect. As a result, the
density of the displayed color can be increased (the transmittance of the
displayed color can be reduced) in the colored state, whereas the
transmittance can be increased in the transmission state. Moreover, when
the first and second liquid crystal layer areas both operate in the
transmission state, a feeling of oppression produced when the screen is
not in use can be reduced.

[0010] It is preferable that the screen according to the aspect of the
invention is capable of operating in a first state in which the first
liquid crystal layer area operates in the scatter state and the second
liquid crystal layer area operates in the colored state, and a second
state in which the first and second liquid crystal layer areas both
operate in the transmission state, and that an image is displayed in the
first liquid crystal layer area that operates in the first state.

[0011] The thus configured screen can display an image that gives a high
contrast sensation.

[0012] In the screen according to the aspect of the invention, it is
preferable that the voltages are applied by common electrodes to the
first and second liquid crystal layer areas.

[0014] In the screen according to the aspect of the invention, it is
preferable that the first state is produced when the voltages are
applied, and that the second state is produced when no voltage is
applied.

[0015] In the configuration described above, an image can be displayed
when the voltages are applied. In this case, the screen is advantageously
used in an application in which the period during which an image is
displayed is shorter than the period during which no image is displayed.

[0016] In the screen according to the aspect of the invention, it is
preferable that the second state is produced when the voltages are
applied, and that the first state is produced when no voltage is applied.

[0017] In the configuration described above, an image can be displayed
when no voltage is applied. In this case, the screen is advantageously
used in an application in which the period during which an image is
displayed is longer than the period during which no image is displayed.

[0018] In the screen according to the aspect of the invention, it is
preferable that the voltages are applied by different electrodes
independently of each other to the first and second liquid crystal layer
areas.

[0019] In the configuration described above, the state of the first liquid
crystal layer area and the state of the second liquid crystal layer area
can be controlled independently of each other.

[0020] In the screen according to the aspect of the invention, it is
preferable that a color displayed in the colored state is black. A
displayed image can thus give a further increased contrast sensation.

[0021] An image display system according to another aspect of the
invention includes the screen according to the aspect of the invention, a
projector that displays an image on the screen, and a controller that
controls operation of driving the screen and the projector.

[0022] The thus configured image display system can give an increased
contrast sensation based on a visual effect of human eyes. In the image
display system according to the aspect of the invention, it is preferable
that the controller instructs the screen to operate in the first state,
in which the first liquid crystal layer area operates in the scatter
state and the second liquid crystal layer area operates in the colored
state, in response to outputting an image signal to the projector.

[0023] In the thus configured image display system, the screen and the
projector are driven in synchronization with each other, whereby the
screen operates in the first state only when an image is displayed on the
screen. That is, when no image is displayed on the screen, the screen
operates in a transparent state (state in which first and second liquid
crystal layer areas both operate in transmission state), whereby a
feeling of oppression produced in this state can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The invention will be described with reference to the accompanying
drawings, wherein like numbers reference like elements.

[0025] FIG. 1 is a plan view of a screen according to a first embodiment
of the invention.

[0027] FIGS. 3A and 3B are plan views for describing the operation of
driving the screen shown in FIG. 1.

[0028]FIG. 4 is a configuration diagram of an image display system into
which the screen shown in FIG. 1 is incorporated.

[0029]FIG. 5 is a plan view showing the configuration of an optical
system of a projector shown in FIG. 4.

[0030]FIG. 6 is a cross-sectional view of a screen according to a second
embodiment of the invention.

[0031]FIG. 7 is a cross-sectional view of a screen according to a third
embodiment of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0032] Screens and image display systems according to preferable
embodiments of the invention will be described below in detail with
reference to the drawings.

First Embodiment

[0033] FIG. 1 is a plan view showing a screen according to a first
embodiment of the invention. FIG. 2 is a cross-sectional view of the
screen shown in FIG. 1. FIGS. 3A and 3B are plan views for describing the
operation of driving the screen shown in FIG. 1. FIG. 4 is a
configuration diagram of an image display system into which the screen
shown in FIG. 1 is incorporated. FIG. 5 is a plan view showing the
configuration of an optical system of a projector shown in FIG. 4.

1. Screen

[0034] A screen 2 includes a pair of transparent substrates 20 and 21, a
pair of transparent electrodes 22 and 23, and a sealing portion 29 that
seals the space between the pair of transparent substrates 20 and 21, as
shown in FIGS. 1 and 2. The transparent electrode 22 is formed on the
surface of the transparent substrate 20 that faces the transparent
substrate 21, and the transparent electrode 23 is formed on the surface
of the transparent substrate 21 that faces the transparent substrate 20.

[0035] The transparent substrates 20 and 21 have a function of supporting
the transparent electrodes 22 and 23 and orientation films 241 and 242,
which will be described later. The transparent substrates 20 and 21 are
made, for example, of, but not necessarily, quartz glass or any other
suitable glass material or polyethylene terephthalate or any other
suitable plastic material. Among the materials described above, in
particular, quartz glass or any other suitable glass material is
preferably used and forms the screen 2 that does not tend to warp, bend,
or otherwise deform but excels in stability. The transparent electrodes
22 and 23 are conductive and made, for example, of an indium tin oxide
(ITO), an indium oxide (IO), or a tin oxide (SnO2).

[0036] The screen 2 has a first liquid crystal layer area S1 set in a
central portion except peripheral portions of the transparent substrates
20 and 21 and a second liquid crystal layer area S2 set at the peripheral
portions of the transparent substrates 20 and 21 having a frame-like
shape and surrounding the first liquid crystal layer area S1 in a plan
view. A partition (seal member) 28 that partitions the screen 2 into the
first liquid crystal layer area S1 and the second liquid crystal layer
area S2 is provided between the pair of transparent substrates 20 and 21.

[0037] The first liquid crystal layer area S1 is an image display section
where an image (video images) is displayed by a projector, which will be
described later, and the second liquid crystal layer area S2 is an area
where a frame that surrounds the image display section is formed. When an
image is displayed in the image display section (first liquid crystal
layer area 51), the frame (second liquid crystal layer area S2) is
colored, for example, black. The colored frame improves the contrast of
the image displayed in the image display section based on a visual effect
of human eyes.

[0038] The width of the second liquid crystal layer area S2 is not limited
to a specific value and is preferably greater than or equal to about 1 cm
but smaller than or equal to about 10 cm depending on the size of the
screen 2. The thus set width makes the black frame large enough to
provide the effect described above and ensures a sufficiently large size
of the first liquid crystal layer area (image display section).

[0039] The pair of orientation films 241 and 242 and a first liquid
crystal layer 25 positioned therebetween are provided between the
transparent substrates 20 and 21 in the first liquid crystal layer area
51. Each of the orientation films 241 and 242 is, for example, a
polyimide film or any other suitable film on which rubbing or any other
suitable orientation process is performed.

[0040] The first liquid crystal layer 25 contains a PDLC (polymer
dispersion liquid crystal) material 251, and the state of the liquid
crystal layer 25 can be switched between a transmission (transparent)
state and a scatter state by changing the magnitude of an electric field
applied thereto. The PDLC 251 includes polymer portions 252 and liquid
crystal portions 253 and can be formed, for example, by mixing a liquid
crystalline monomer or any other suitable polymer precursor with a liquid
crystal molecule. To form the PDLC 251, the mixture is allowed to undergo
an orientation process by using the orientation films 241 and 242 and so
irradiated with ultraviolet light or any other form of energy that the
liquid crystalline monomer is polymerized. The thus polymerized and
oriented liquid crystalline monomer forms the polymer portions 252 having
an orientation anchoring force. The liquid crystal molecule is separated
from the polymer portions 252 in a phase separation process to form the
liquid crystal portions 253, which are oriented by the orientation
anchoring force of the polymer portions 252.

[0041] The PDLC 251 in the present embodiment is of reverse type, which
means that the first liquid crystal layer 25 operates in the transmission
state, in which the first liquid crystal layer 25 is transmissive, in a
state in which no voltage is applied, whereas the first liquid crystal
layer 25 operates in the scatter state, in which the first liquid crystal
layer 25 is diffusive, in a state in which a voltage is applied.
Specifically, in the no voltage applied state, since the liquid crystal
portions 253 are oriented in the same direction as the polymer portions
252, the refractive index continuously changes at the boundaries between
the liquid crystal portions 253 and the polymer portions 252 (the
refractive index of the liquid crystal portions 253 is substantially
equal to that of the polymer portions 252) and light incident on the PDLC
251 is hardly diffused but directly exits out thereof or the screen 2
operates in the transmission state. Conversely, in the voltage applied
state, the azimuth of the polymer molecules in the polymer portions 252
does not change, whereas the azimuth of the liquid crystal molecules in
the liquid crystal portions 253 changes in accordance with the electric
field, whereby the refractive index discontinuously changes at the
boundaries between the polymer portions 252 (the refractive index of the
liquid crystal portions 253 is different from that of the polymer
portions 252) and the liquid crystal portions 253 and the incident light
is scattered before it exits out of the PDLC 251 or the screen 2 operates
in the scatter state.

[0042] A pair of orientation films 261 and 262 and a second liquid crystal
layer 27 positioned therebetween are provided between the transparent
substrates 20 and 21 in the second liquid crystal layer area S2. The
second liquid crystal layer 27 is what is called a guest-host liquid
crystal layer containing a liquid crystal (host liquid crystal) material
271 and a dichromatic dye 272. The liquid crystal material 271, the
orientation of which is changed when an electric field is present, has a
function of controlling the orientation of the dichromatic dye 272
dissolved as a guest. The liquid crystal material 271 is not limited to a
specific one and may, for example, be a nematic liquid crystal material
or a smectic liquid crystal material.

[0043] On the other hand, the dichromatic dye 272 is a dye molecule that
is dissolved in the liquid crystal material 271 and absorbs light of a
specific color by a variable amount according to the orientation of the
molecule. In the following description, the axis of the dichromatic dye
272 along which light of a specific color is absorbed is called a "light
absorption axis," and light that intersects the light absorption axis is
absorbed. The dichromatic dye 272 in the present embodiment has an
elongated rod-like shape having a major axis and a minor axis, and the
major axis of the dichromatic dye 272 is the light absorption axis.

[0044] The dichromatic dye 272 in the second liquid crystal layer 27
preferably has the following dyes mixed therein: a first dichromatic dye
having an absorption maximum in a yellow region, a second dichromatic dye
having an absorption maximum in a magenta region, and a third dichromatic
dye having an absorption maximum in a cyan region. The dichromatic dye
272 having the first, second, and third dichromatic dyes mixed at an
appropriately selected ratio can operate in a colored state that displays
a desired color. The color displayed in the colored state is not limited
to a specific color but is preferably black.

[0045] Examples of the dichromatic dye 272 may include an azoic dye, an
anthraquinone dye, a perylene dye, a merocyanine dye, an azomethine dye,
a phthaloperylene dye, an indigo dye, an azulene dye, a dioxazine dye, a
polythiophene dye, and a phenoxazine dye.

[0046] The second liquid crystal layer 27 in the present embodiment is of
VA (vertical alignment) type, which means that the second liquid crystal
layer 27 operates in the transmission state, in which the second liquid
crystal layer 27 is transmissive, in a state in which no voltage is
applied, whereas the second liquid crystal layer 27 operates in the
colored state, in which the second liquid crystal layer 27 displays a
predetermined color, in a state in which a voltage is applied.
Specifically, in the no voltage applied state, the liquid crystal
material 271 is oriented vertically, and the dichromatic dye 272 follows
the vertical orientation of the liquid crystal material 271 or the screen
2 operates in the transmission state. Conversely, in the voltage applied
state, the liquid crystal material 271 is oriented horizontally, and the
dichromatic dye 272 follows the horizontal orientation of the liquid
crystal material 271 or the screen 2 operates in the colored (black)
state. It is noted that the second liquid crystal layer 27 is not limited
to a VA liquid crystal layer and may be any liquid crystal layer that
operates in the transmission state in the no voltage applied state
whereas operating in the colored state in the voltage applied state.

[0047] In the thus configured second liquid crystal layer 27, the
orientation of the dichromatic dye 272 can be reliably changed based on
the guest-host effect, whereby the transmission state and the colored
state can be reliably and clearly switched. That is, the transmittance in
the transmission state can be increased, whereas the light absorbance in
the colored state can be increased.

[0048] In the thus configured screen 2, the pair of common transparent
electrodes 22 and 23 create an electric field acting on the first liquid
crystal layer area S1 and the second liquid crystal layer area S2. The
screen 2 can therefore operate in one of the following states at a time:
an electric field created state in which a voltage is applied between the
transparent electrodes 22 and 23 so that an electric field acts on the
first liquid crystal layer area S1 and the second liquid crystal layer
area S2 and a no electric field created state in which no voltage is
applied between the transparent electrodes 22 and 23 so that no electric
field acts on the first liquid crystal layer area S1 or the second liquid
crystal layer area S2.

[0049] The "no electric field created state" described above includes not
only a state in which no electric field is crated at all but also a state
in which a voltage smaller than the voltage applied in the electric field
created state is applied between the pair of transparent electrodes 22
and 23 so that an electric field less intense than that in the electric
field created state is created.

[0050] In the electric field created state, the first liquid crystal layer
area S1 operates in the scatter state and the second liquid crystal layer
area S2 operates in the colored state (the overall state is called a
"first state"), as shown in FIG. 3A. An image can therefore be displayed
in the first liquid crystal layer area S1. Further, the displayed image
can be surrounded by the black frame formed of the second liquid crystal
layer area S2. Conversely, in the no electric field created state, the
first liquid crystal layer area S1 and the second liquid crystal layer
area S2 both operate in the transmission state (the overall state is
called a "second state"), as shown in FIG. 3B. The screen 2 thus operates
in the transparent state. The screen 2, which is capable of switching its
state between the first and second states, provides the following
advantageous effects.

[0051] First, the screen 2 can be transparent when the screen 2 is not in
use and is driven to operate in the second state. A feeling of oppression
produced by the screen 2 can therefore be reduced, for example, when the
screen 2 is used in a space where the user lives.

[0052] In particular, since the second liquid crystal layer area S2 of the
screen 2 contains no polymer, the dichromatic dye can be appropriately
moved based on a guest-host effect. As a result, the density of the
displayed color can be increased (the transmittance of the displayed
color can be reduced) in the colored state, whereas the transmittance can
be increased in the transmission state. Further, since the first liquid
crystal layer area S1 contains no dichromatic dye, the transmittance can
be further increased in the transmission state.

[0053] Second, when the screen 2 is in use, the screen 2 is driven to
operate in the first state, whereby the second liquid crystal layer area
S2 around the first liquid crystal layer area S1 works as a colored
frame. As a result, an image displayed in the first liquid crystal layer
area S1 gives an improved contrast sensation based on a visual effect of
human eyes. In particular, the effect is more noticeable when the
displayed color in the colored state is black.

[0054] Further, in the screen 2 according to the present embodiment, which
is so configured that the common electrodes (transparent electrodes 22
and 23) apply a voltage to the first liquid crystal layer area S1 and the
second liquid crystal layer area S2, the first state is achieved simply
by applying a voltage to the transparent electrodes 22 and 23. The
operation of driving the screen 2 is therefore more readily controlled.
It is noted that the screen 2 described above is preferably used in an
application in which the period during which an image is displayed on the
screen 2 (period during which screen 2 operates in first state) is
shorter than the period during which no image is displayed on the screen
2 (period during which screen 2 operates in second state). The screen 2
can thus be driven in a power-saving mode.

2. Image Display System

[0055] An image display system 100 into which the screen 2 is incorporated
will next be described.

[0056] The image display system 100 includes the screen 2, a projector 300
that displays an image on the screen 2, and a controller 400 that
controls the operation of driving the screen 2 and the projector 300, as
shown in FIG. 4. In the image display system 100, an image is projected
from the side of the screen 2 that faces away from a viewer on the rear
surface of the screen (surface facing away from viewer). An image may
alternatively be projected from the side of the screen 2 that faces the
viewer on the front surface of the screen 2 (surface facing viewer).

[0057] The projector 300 is not limited to a specific one and can be any
projector that can display an image on the screen 2. For example, an
illumination projection projector that enlarges and projects an image
formed by a spatial light modulator on the screen 2 or a scanning
projector that scans the screen 2 with light to form an image may be
used. An example of the projector 300 will be shown below.

[0058]FIG. 5 is a plan view showing the configuration of an optical
system of the projector 300. The projector 300 includes an illumination
system 310, a color separation system 320, parallelizing lenses 330R,
330G, and 330B, spatial light modulators 340R, 340G, and 340B, and a
cross dichroic prism 350, which is a light combiner, as shown in FIG. 5.

[0059] The illumination system 310 includes a light source 311, a
reflector 312, a first lens array 313, a second lens array 314, a
polarization conversion element 315, and a superimposing lens 316.

[0060] The light source 311 is an ultra-high pressure mercury lamp, and
the reflector 312 is formed of a parabolic mirror. A divergent light flux
emitted from the light source 311 is reflected off the reflector 312 and
forms a substantially parallelized light flux, which is directed toward
the first lens array 313. The light source 311 is not limited to an
ultra-high pressure mercury lamp but may alternatively be, for example, a
metal halide lamp. Further, the reflector 312 is not limited to a
parabolic mirror but may alternatively be an ellipsoidal mirror reflector
with a parallelizing concave lens disposed on the side where the
light-exiting surface thereof is present.

[0061] Each of the first lens array 313 and the second lens array 314 is
formed of lenslets arranged in a matrix. The light flux emitted from the
light source 311 is divided by the first lens array 313 into a plurality
of thin partial light fluxes, which are superimposed on the surfaces of
the three spatial light modulators 340R, 340G, and 340B, which are
illuminated with light traveling through the second lens array 314 and
the superimposing lens 316.

[0062] The polarization conversion element 315 has a function of aligning
randomly polarized light fluxes with each other to produce linearly
polarized light oscillating in a single direction (S-polarized light or
P-polarized light). In the present embodiment, the polarization
conversion element 315 produces S-polarized light because the intensity
thereof is not greatly reduced in the color separation system 320.

[0063] The color separation system 320 has a function of separating the
light flux having exited out of the illumination system 310 (S-polarized
light) into red (R), green (G), and blue (B), three color light fluxes.
To this end, the color separation system 320 includes a B-light
reflecting dichroic mirror 321, an RG-light reflecting dichroic mirror
322, a G-light reflecting dichroic mirror 323, and reflection mirrors 324
and 325.

[0064] Among the light fluxes having exited out of the illumination system
310, the B-light component is reflected off the B-light reflecting
dichroic mirror 321, further reflected off the reflection mirror 324 and
a reflection mirror 361, and reaches the parallelizing lens 330B. On the
other hand, among the light fluxes having exited out of the illumination
system 310, the G-light and R-light components are reflected off the
RG-light reflecting dichroic mirror 322, further reflected off the
reflection mirror 325, and reaches the G-light reflecting dichroic mirror
323. The G-light component of the light having reached the G-light
reflecting dichroic mirror 323 is reflected off the G-light reflecting
dichroic mirror 323 and a reflection mirror 362 and reaches the
parallelizing lens 330G, whereas the R-light component of the light
having reached the G-light reflecting dichroic mirror 323 passes through
the G-light reflecting dichroic mirror 323, is reflected off a reflection
mirror 363, and reaches the parallelizing lens 330R.

[0065] The parallelizing lenses 330R, 330G, and 330B are so configured
that the plurality of partial light fluxes having exited out of the
illumination system 310 are substantially parallelized and illuminate the
spatial light modulators 340R, 340G, and 340B in a satisfactory manner.

[0066] The R light having passed through the parallelizing lens 330R
reaches the spatial light modulator 340R. The G light having passed
through the parallelizing lens 330G reaches the spatial light modulator
340G. The B light having passed through the parallelizing lens 330B
reaches the spatial light modulator 340B.

[0067] The spatial light modulator 340R, which modulates the R light in
accordance with an image signal, is a transmissive liquid crystal display
device. A liquid crystal panel (not shown) provided in the spatial light
modulator 340R includes two transparent substrates and a liquid crystal
layer sealed therebetween for modulating light in accordance with the
image signal. The R light modulated by the spatial light modulator 340R
is incident on the cross dichroic prism 350, which is a light combining
system. The configuration and function of each of the spatial light
modulators 340G and 340B are the same as those of the spatial light
modulator 340R.

[0068] The cross dichroic prism 350 is formed by bonding four triangular
prisms into a rectangular column having a substantially square
cross-sectional shape, and dielectric multilayer films 351 and 352 are
formed along the X-shaped bonded surfaces. The dielectric multilayer film
351 transmits G light and reflects R light, and the dielectric multilayer
film 352 transmits G light and reflects B light. The cross dichroic prism
350 combines the modulated color light fluxes having exited from the
spatial light modulators 340R, 340G, and 340B and impinged on light
incident surfaces 350R, 350G, and 350B to form video image light
representing a color image and directs the video image light to a
projection optical unit 360.

[0070] The controller 400 includes an image signal output section 410 that
outputs an image signal to the projector 300 and a screen control section
420 that controls the operation of driving the screen 2 (ON/OFF), as
shown in FIG. 4. The projector 300, when it receives an image signal from
the image signal output section 410, outputs the video image light L
based on the image signal. The thus configured controller 400 instructs
the screen control section 420 to control the operation of driving the
screen 2 in response to instructing the image signal output section 410
to output the image signal to the projector 300. Specifically, in a state
in which the image signal output section 410 outputs no image signal, the
controller 400 instructs the screen control section 420 to drive the
screen 2 in the second state, that is, the transmission (transparent)
state. Conversely, in a state in which the image signal output section
410 outputs an image signal, the controller 400 instructs the screen
control section 420 to drive the screen 2 in the first state, that is,
the first liquid crystal layer area S1 to operate in the scatter state
and the second liquid crystal layer area S2 to operate in the colored
state.

[0071] The control described above allows the screen 2 to operate in the
second state when the projector 300 outputs no video image light L, that
is, when no image to be displayed on the screen 2 is present. On the
other hand, the control described above allows the screen 2 to operate in
the first state when the projector 300 outputs the video image light L,
whereby an image corresponding to the video image light L can be
displayed in the first liquid crystal layer area S1 of the screen 2. That
is, the simple control described above allows the screen 2 to operate in
the transmission state whenever no image is displayed on the screen 2,
whereby power can be saved and a feeling of oppression produced in a
space where the viewer lives can be reduced.

Second Embodiment

[0072] A screen according to a second embodiment of the invention will
next be described.

[0073]FIG. 6 is a cross-sectional view of the screen according to the
second embodiment of the invention.

[0074] The screen according to the second embodiment will be described
below primarily on differences from the embodiment described above, and
similar items will not be described.

[0075] The screen according to the second embodiment of the invention is
substantially the same as that according to the first embodiment
described above and only differs therefrom in terms of drive mode. The
same components as those in the first embodiment described above have the
same reference characters. In a screen 2A according to the present
embodiment, the PDLC 251 that forms the first liquid crystal layer 25 is
of normal type, as shown in FIG. 6. The first liquid crystal layer 25
therefore operates in the scatter state in the no voltage applied state,
whereas operating in the transmission state in the voltage applied state.
On the other hand, the second liquid crystal layer 27 is of TN (twisted
nematic) type. The second liquid crystal layer 27 therefore operates in
the colored state in the no voltage applied state, whereas operating in
the transmission state in the voltage applied state. The second liquid
crystal layer 27 is not necessarily of TN type and may alternatively be
of any type that provides the colored state in the no voltage applied
state whereas operating in the transmission state in the voltage applied
state.

[0076] The thus configured screen 2A can operate in one of the following
states at a time: an electric field created state in which a voltage is
applied between the transparent electrodes 22 and 23 and an electric
field acts on the first liquid crystal layer area S1 and the second
liquid crystal layer area S2 and a no electric field created state in
which no voltage is applied between the transparent electrodes 22 and 23
and no electric field acts on the first liquid crystal layer area S1 or
the second liquid crystal layer area S2.

[0077] In the no electric field created state, the first liquid crystal
layer area S1 operates in the scatter state, and the second liquid
crystal layer area S2 operates in the colored state. An image can
therefore be displayed in the first liquid crystal layer area S1.
Further, the displayed image can be surrounded by the black frame formed
of the second liquid crystal layer area S2. Conversely, in the electric
field created state, the first liquid crystal layer area S1 and the
second liquid crystal layer area S2 both operate in the transmission
state. The entire screen 2A thus operates in the transparent state. The
second embodiment described above also provides the same advantageous
effects as those provided by the first embodiment. It is noted that the
screen 2A is suitably used in an application in which the period during
which an image is displayed on the screen 2A (period during which screen
2A operates in first state) is longer than the period during which no
image is displayed on the screen 2A (period during which screen 2A
operates in second state). The screen 2A can thus be driven in a
power-saving mode.

Third Embodiment

[0078] A screen according to a third embodiment of the invention will next
be described.

[0079]FIG. 7 is a cross-sectional view of the screen according to the
third embodiment of the invention.

[0080] The screen according to the third embodiment will be described
below primarily on differences from the embodiments described above, and
similar items will not be described.

[0081] The screen according to the third embodiment of the invention is
substantially the same as that according to the first embodiment
described above and only differs therefrom in terms of electrode
configuration. The same components as those in the first embodiment
described above have the same reference characters.

[0082] A screen 2B includes a pair of first transparent electrodes 221 and
231 that sandwich the first liquid crystal layer area S1 and a pair of
second transparent electrodes 222 and 232 that sandwich the second liquid
crystal layer area S2, as shown in FIG. 7. In other words, the
transparent electrodes 22 and 23 are divided into portions in the first
liquid crystal layer area S1 and portions in the second liquid crystal
layer area S2.

[0083] In the screen 2B, voltage application between the pair of first
transparent electrodes 221 and 231 and voltage application between the
pair of second transparent electrodes 222 and 232 can be performed
independently of each other. The state of the first liquid crystal layer
area S1 and the state of the second liquid crystal layer area S2 can
therefore be controlled independently of each other.

[0084] The screen 2B can operate in one of the following states at a time
as in the first embodiment described above: the first state, in which the
first liquid crystal layer area S1 operates in the scatter state and the
second liquid crystal layer area S2 operates in the colored state, and
the second state, in which the first liquid crystal layer area S1 and the
second liquid crystal layer area S2 both operate in the transmission
state. Further, the screen 2B according to the present embodiment can
operate in a third state in which the second liquid crystal layer area S2
operates in the colored state as in the first state but the first liquid
crystal layer area S1 scatters light at a rate between those in the first
and second states (intermediate rate), in other words, a state in which
the degree of light scattering in the first liquid crystal layer area S1
is changed from that in the second state. The degree of light scattering
in the third state can be adjusted continuously or discretely in multiple
steps by changing the voltage applied between the transparent electrodes
221 and 231.

[0085] The third state is advantageous, for example, when the background
behind the screen 2B and an image displayed in the first liquid crystal
layer area S1 are desired (allowed) to be visible at the same time. That
is, since the first liquid crystal layer area S1 is semitransparent in
the third state, the background behind the first liquid crystal layer
area S1 can be visible and an image can be displayed in the first liquid
crystal layer area at the same time. Further, since the second liquid
crystal layer area S2 operates in the colored state (black state) as in
the first state, an image displayed in the first liquid crystal layer
area can give an increased contrast sensation.

[0086] The third state is not necessarily used in a specific application
and can be used, for example, in a case where an exhibition product is
placed behind the screen 2B and information on the exhibition product is
displayed in the first liquid crystal layer area of the screen 2B. The
information can thus be effectively displayed without obstructing the
observation of the exhibition product.

[0087] The third embodiment described above also provides the same
advantageous effects as those provided by the first embodiment. In the
screen 2B according to the present embodiment, since the state of the
first liquid crystal layer area S1 and the state of the second liquid
crystal layer area S2 can be controlled independently of each other, the
types of the first liquid crystal layer area S1 and the second liquid
crystal layer area S2 can be combined in any way, unlike in the first and
second embodiments described above. That is, the first liquid crystal
layer area S1 may be of reverse type and the second liquid crystal layer
area S2 may be of VA type as in the first embodiment, or the first liquid
crystal layer area S1 may be of normal type and the second liquid crystal
layer area S2 may be of TN type as in the second embodiment.
Alternatively, the first liquid crystal layer area S1 may be of reverse
type and the second liquid crystal layer area S2 may be of TN type, or
the first liquid crystal layer area S1 may be of normal type and the
second liquid crystal layer area S2 may be of VA type.

[0088] The screens and the image display system according to the
embodiments of the invention have been described above with reference to
the drawings, but the invention it not limited thereto. The configuration
of each of the components can be replaced with an arbitrary configuration
having the same function. Further, other arbitrary components may be
added to the invention. Moreover, the embodiments may be combined with
each other as appropriate.